In the automotive electronics packaging industry, wire bonding is used as a means for making electrical connections between electronic components and a stamped lead frame that often is insert molded within an injection molded plastic housing. A wire is bonded with specialized equipment, known as a wire bonder, to the electronic component and to the stamped lead frame. The wire bonder uses a pattern recognizing vision system to identify features within the molded housing from which the location of the wire bonding sites is determined. The features to be recognized must have a certain level of consistency in order for the wire bonder to successfully identify the feature and its location. Software then calculates the expected location of the bonding site relative to the detected location of the feature, and the system automatically creates a bond at the calculated location. This process is commonly referred to as “pattern recognition”.
Wire bonders work at relatively high rates of speed both when performing pattern recognition and when doing the actual wire bonding steps. Inconsistency in the visual quality of the pattern recognition features can lead to misplacing wire bonds, which thereafter can result in assembly-line stoppages. Accordingly, consistent and rapid pattern recognition is a desirable feature. Consistent pattern recognition requires consistency in manufacture from one part to the next so that the features to be recognized by the pattern recognition system do not vary significantly from one part to the next part.
In automotive sensors, a stamped lead frame often is secured in a plastic sensor housing, and wires are subsequently bonded to the lead frame. In an accepted process, the stamped lead frame is insert-molded into the plastic of the housing. During the molding process, the molten plastic typically molds up to the edge of the stamping. An outer edge of the stamping commonly is used as a pattern recognition feature. If, during the molding process, the plastic flows up to and over the top edge of the insert molded lead frame, the interface between plastic and the lead frame edge can be inconsistent or jagged. A jagged, inconsistent edge creates recognition difficulties for the pattern recognition system and can result in defective wire bonds.
It is desirable and advantageous to have a pattern recognition feature that is consistent from one part to another part so that recognition of the feature is easy and consistent. To produce a consistently clean edge for pattern recognition, it is desirable to prevent plastic from molding up to the edge intended to be used for pattern recognition.